1. Field of the Invention
The present invention relates to a turbo-molecular pump for evacuating gas with a rotor that rotates at a high speed.
2. Description of the Related Art
FIG. 21 of the accompanying drawings shows a conventional turbo-molecular pump. As shown in FIG. 21, the conventional turbo-molecular pump comprises a rotor R and a stator S which are housed in a pump casing 14. The rotor R and the stator S jointly make up a turbine blade pumping section L1 and a thread groove pumping section L2. The stator S comprises a base 15, a stationary cylindrical sleeve 16 vertically mounted centrally on the base 15, and stationary components of the turbine blade pumping section L1 and the thread groove pumping section L2. The rotor R mainly comprises a main shaft 10 inserted coaxially in the stationary cylindrical sleeve 16, and a rotary cylindrical sleeve 12 mounted on the main shaft 10 and disposed around the stationary cylindrical sleeve 16.
Between the main shaft 10 and the stationary cylindrical sleeve 16, there are provided a drive motor 18, an upper radial magnetic pole 20 disposed above the drive motor 18, and a lower radial magnetic pole 22 disposed below the drive motor 18. An axial bearing 24 is disposed at a lower portion of the main shaft 10, and comprises a target disk 24a mounted on the lower end of the main shaft 10, and upper and lower electromagnets 24b provided on the stator side. By this magnetic bearing system, the rotor R can be rotated at a high speed under 5-axis active control.
The rotary cylindrical sleeve 12 has rotor blades 30 integrally disposed on an upper outer circumferential portion thereof. In the pump casing 14, there are provided stator blades 32 disposed axially alternately with the rotor blades 30. The rotor blades 30 and the stator blades 32 jointly make up the turbine blade pumping section L1 for evacuating gas by way of an interaction between the rotor blades 30 and the stator blades 32.
The thread groove pumping section L2, which is disposed downwardly of the turbine blade pumping section L1, includes a thread groove section 34 of the rotary cylindrical sleeve 12 which has thread grooves 34a defined in an outer circumferential surface thereof and surrounds the stationary cylindrical sleeve 16. The stator S has a spacer 36 disposed around the thread groove section 34. The thread groove pumping section L2 evacuates gas by way of a dragging action of the thread grooves 34a in the thread groove section 34 which rotates at a high speed in unison with the rotor R. The stator blades 32 have outer edges clamped by either stator blade spacers 38 or the stator blade spacer 38 and the spacer 36.
With the thread groove pumping section L2 disposed downstream of the turbine blade pumping section L1, the turbo-molecular pump is of the wide range type capable of handing a wide range of rates of gas flows. In the conventional turbo-molecular pump shown in FIG. 21, the thread grooves 34a of the thread groove pumping section L2 are defined in the rotor R. However, the thread grooves of the thread groove pumping section L2 may be defined in the stator S.
In such a turbo-molecular pump, if the rotor R is broken due to corrosion or the like, then fragments of the rotor R may enter an intake port 14a of the pump casing 14. When fragments of the rotary cylindrical sleeve 12 or the rotor blades 30 which have large kinetic energy are introduced into the chamber of a processing apparatus that is connected to the intake port 14a of the pump casing 14 through a flange 14b, the processing apparatus may be broken or products that are being processed by the processing apparatus may be damaged, and the overall evacuating system may be destroyed, tending to cause a harmful processing gas to leak into the surrounding environment.
It is therefore an object of the present invention to provide a highly safe turbo-molecular pump which can prevent rotor fragments from damaging the chamber in a processing apparatus and products being processed by the processing apparatus even when a rotor of the turbo-molecular pump is broken, and which can be replaced in its entirety in case of destruction for quickly making the processing apparatus reusable.
According to the present invention, there is provided a turbo-molecular pump comprising a casing having an intake port, a stator fixedly mounted in the casing, a rotor supported in the casing for rotation relatively to the stator, the stator and the rotor serving as at least one of a turbine blade pumping section and a thread groove pumping section for evacuating gas, and a scattering prevention member for preventing fragments of the rotor from being scattered through the intake port.
If the rotor is broken, then fragments of the rotor, e.g., a rotary cylindrical sleeve and rotor blades, or fragments of the stator, e.g., stator blades, are blocked by the scattering prevention member, or lose the kinetic energy toward the intake port. Therefore, the scattering prevention member is effective to prevent those fragments from damaging the chamber in a processing apparatus connected to the intake port or devices and products being processed in the chamber. The scattering prevention member may be mounted on a stationary member such as the casing, or the rotor.
The rotor comprises rotor blades and the stator comprises stator blades, and the scattering prevention member comprises at least part of the rotor blade or the stator blade. Therefore, at least part of the rotor blade or the stator blade has a fragment shield function.
The scattering prevention member includes at least one protrusion projecting radially inwardly from an inner surface of the intake port. If the rotor is broken, rotor fragments collide with the protrusion, and are prevented from being scattered through the intake port or kinetic energy of the rotor fragments is reduced.
The scattering prevention member is made of a high-strength material and/or a high-energy absorbing material. The high-strength material may be stainless steel, titanium alloy, or the like which is stronger than aluminum. The high-energy absorbing material may be made of a relatively soft metal material such as lead, a polymer material, or a composite material thereof, and shaped so as to be effective to absorb shocks, e.g., shaped into a honeycomb structure or an assembly of spherical members.
The scattering prevention member has a shock absorbing structure. The shock absorbing structure is effective to absorb the kinetic energy of rotor fragments which collide with the scattering prevention member for better protection of the chamber in the processing apparatus that is connected to the intake port.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.